CHARACTERISTICS OF HEAVILY CARBON-DOPED GAAS BY LPMOCVD AND CRITICAL LAYER THICKNESS

The carbon-doping characteristics of GaAs epilayers have been investigated by varying the growth parameters - V/III ratio and growth temperature. We have obtained the highest 1.4 x 10(20) cm-3 hole concentration with hole mobility 42 cm2/V.s without using intentional doping source gases. The carbon incorporation increased with increasing growth temperature up to the critical temperature and above this temperature the carbon incorporation decreased. This critical temperature depends on input TMG flow rate. The peak energy of the PL intensity distribution was shifted to lower energy (red shift) and the full width at half maximum (FWHM) increased with increasing hole concentration. The (400) diffraction peak of the carbon-doped GaAs epilayer was split from the substrate GaAs peak. The split angle was 191.25 arc sec for the carbon-doped GaAs with 9 X 10(19) cm-3 hole concentration. We also have discussed the relationship between carbon-doping concentration and critical layer thickness (L(C)) by an excess stress model. The excess stress at which partial strain relief became observable was sigma(exc)/mu = 0.0021. Thus we identified this excess stress as the critical excess stress for carbon-doped GaAs epilayers. If the excess stress was greater than this, the epilayers showed the surface cross-hatching.